An ASON is a network that enables the automatic delivery of transport services, including leased-line connections and other transport services, such as switched and soft-permanent optical connections. The ASON provides a framework for protection switching and reutilization is articulated by Generalized Multi-Protocol Label Switching (GMPLS) or the like. In an ASON, each network node is equipped with a control plane that sets up and releases connections, and may restore a connection in the case of a failure. These control planes may be thought of as switches. ITU-T Recommendation G.8080, “Architecture for the automatically switched optical network (ASON),” describes the set of control plane components that are used to manipulate the transport network resources, including the setting up, maintaining, and releasing of connections. A switched connection is set up and released from a Network Management System (NMS) that uses network generated signaling and routing protocols to establish the connection. Connections in an ASON are typically Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) or Optical Transport Network (OTN). The architectures for these connections are described in ITU-T Recommendations G.803 and G.872, respectively.
Referring to FIG. 1, in an ASON 10, a connection may originally be requested from either a client device 12a,12b (in which case the connection is referred to as a Switched Connection (SC) 14) or a NMS interface 16 (in which case the connection is referred to as a Soft-Permanent Connection (SPC) 18). In this exemplary embodiment, the ASON 10 includes three control domains: Domain A 20, Domain B 22, and Domain C 24, and six Network Elements (NEs) 30,32,34,36,38,40. The requesting entity may be part of any control domain 20,22,24 or part of an external network.
Domain A 20 includes NEs 30,32 as Border Nodes (BNs), Domain B 22 includes NEs 34,36 as BNs, and Domain C 24 includes NEs 38,40 as BNs. Each of these control domains 20,22,24 may include additional NEs between the BNs (not illustrated), and these are referred to as Intermediate Nodes (INs). In this exemplary embodiment, the clients 12a,12b connect to the NEs 30,40, respectively, via an Optical User-to-Network Interface (O-UNI). This enables control plane interoperability between the clients 12a,12b and the control domains 20,22,24. The control domains 20,22,24 interconnect via External Network-to-Network Interfaces (E-NNIs)—between NEs 32 and 34 for the interconnection of Domain A 20 and Domain B 22, and between NEs 36 and 38 for the interconnection of Domain B 22 and Domain C 24.
Sub-Network Connections (SNCs) 42,44,46 originate from one BN of a network (i.e. control domains 20,22,24) and terminate on another BN of the same network (i.e. control domains 20,22,24). In FIG. 1, SNC 42 originates from NE 30 and terminates on NE 32, SNC 44 originates from NE 34 and terminates on NE 36, and SNC 46 originates from NE 38 and terminates on NE 40. The links between NEs 32 and 34, and 36 and 38 are E-NNI links. The end NEs 30,40 across the control domains 20,22,24 may be SC clients that originate and terminate the SC 14. Typically, the SC 14 or SPC 18 includes multiple SNCs 42,44,46. The connections 14,18 may also include SONET/SDH services or Ethernet resources.
With the increase in demand for data traffic, ASONs are rapidly growing in size and total bandwidth, reaching hundreds of nodes. This increase in size and total bandwidth results in a large volume of messages being handled by the control planes. Processing power must increase and/or the efficiency of routing algorithms must improve if network restoration performance is to be maintained. Being finite, processing power and the efficiency of routing algorithms represent a real limitation on the scalability of a mesh network. This scalability problem may easily be imagined for lines that carry multiple SNCs in a large network. The failure of such a line requires the re-routing of all SNCs.
To solve this problem, mesh restoration may be combined with conventional line based protection at the server or line layer. Server layer protection is typically applied on the SONET/SDH line, or Optical Transport Unit/Optical Data Unit (OTUk/ODUk) path if the optical transport layer is used. Combining mesh restoration with conventional lines based protection increases performance and scalability, but requires significant network planning and introduces topology limitations. All of these line based methods require predetermined protection bandwidth and are topology dependent (i.e. ring based or point-to-point).
Combining SONET/SDH and OTN mesh networks is possible given the current state-of-the-art, but requires a clear demarcation and fixed hand-off between the two. This is even more undesirable than the former case, as these fixed hand-offs require additional protection.
Thus, what is needed in the art are methods and systems that provide a mesh restorable OTN server layer that carries an aggregate of mesh restorable SONET/SDH SNCs, without designating SONET/SDH/OTN hand-off ports or work/protect lines.